class_docstr: Learning Without Forgetting.
  
  The method applies knowledge distilllation to mitigate forgetting.
  The teacher is the model checkpoint after the last experience.
docstr: Add distillation loss
docstr_tok: ["Add","distillation","loss"]
code: def __call__(self, mb_x, mb_pred, model):
      """
      Add distillation loss
      """
      alpha = (
          self.alpha[self.expcount]
          if isinstance(self.alpha, (list, tuple))
          else self.alpha
      )
      return alpha * self._lwf_penalty(mb_pred, mb_x, model)
  
imports: import copy
  from collections import defaultdict
  from typing import List
  import torch
  import torch.nn.functional
  from avalanche.models import MultiTaskModule, avalanche_forward
label_desc: Use image node_id 4 for calling the LearningWithoutForgetting obj's underlying member method code with example usage: obj.__call__(mb_x, mb_pred, model) and returns: unknown